OpenBSD compatibility.

Patch below adds support for OpenBSD.
The sudoers file is taken from a -current OpenBSD system, with just the added 
#includedir /etc/sudoers.d 
statement.

Further changes to params.pp for OpenBSD support, mostly copied from freebsd.
The little change to package.pp was necessary, because sudo is part of the base installation, therefore no package needed to be installed.